This invention relates to the art of electronic tube devices of the electron beam type, and more particularly to a new and improved method and apparatus for controlling the voltage on one or more electrodes in these devices such as cathode ray pin tubes.
When it is desired to vary the voltage of an electrode in a vacuum tube this has been done by means of a lead from the electrode through the tube envelope to an external circuit. When many electrodes of the same device must be controlled, this approach requires a lead configuration which is difficult or even impossible owing to the large number of vacuum seals required in the tube envelope and mechanical constraints imposed by the connecting leads. It therefore would be highly desirable to provide control of one or more electrodes of a vacuum tube device in a manner obviating the need to have leads connected to each electrode and extending through the tube envelope.
The foregoing considerations are particularly appropriate for cathode ray pin tubes, also known as conductive face plate cathode ray tubes, which are used to transfer information typically in electrostatic printing. Briefly, such devices include a face plate having an array of closely-spaced conductive pins which extend through the faceplate and which become charged when the electron beam impinges upon the pin and thus can be used to transfer information. In an electrostatic printer a dielectric medium such as a belt accepts a charge from the pins of the device to form a latent image of the information which thereafter is developed by toner and transferred to paper. It is important to control the voltage on the individual pins of the device because pin voltage anomalies can adversely affect the ultimate printing quality.